Pro-choice campaigners and their political allies are coming together to stage a fightback against what they view as attempts by the Christian right and social conservatives to chip away at established abortion rights as MPs stage a cross-party attempt to tighten legislation.

It comes as a "rising tide of opposition and concern" is emerging about the agenda of figures in the government, according to Diane Abbott, the shadow minister for public health, who is to address a pro-choice meeting in London on Monday.

The gathering will bring together women's rights activists, trade unionists and others and is one of a number being organised nationwide in which liberal-left bloggers are playing a key role.

Life, which is opposed to abortion in all circumstances and favours an abstinence-based approach to sex education, is expected to take up its seat at the second meeting of the forum this week.

BPAS said it had been "disinvited" after attending the forum's first meeting in January. The government maintains the panel reflects a "wide range of interests and views".

Pro-choice supporters, however, are particularly concerned about an amendment to the health and social care bill that would create a new precondition for women having an abortion to receive advice and counselling from an organisation that does not carry out terminations. The amendment is part of a campaign called Right to Know, launched by Nadine Dorries, a Conservative MP, and Frank Field, a former Labour minister.

"We cannot allow Nadine Dorries and some of the anti-abortion groups currently advising the government to turn the clock back for millions of women," said Abbott.

"Mainstream medical opinion is united in its agreement that, when carried out in a legal setting where sterile facilities are available, abortion is a safe procedure carrying a low risk of complications.

"And we must not underestimate the chilling news that the government has appointed anti-abortion group Life to their expert advisory group on sexual health. This appointment, coupled with the retraction of an invite to the British Pregnancy Advisory Service, one of the UK's leading abortion providers, signals a dangerous move."

She added: "Increasingly, people up and down the country are looking to take a stand against what they see as an attempt to chip away at abortion access for women in England, Scotland and Wales.

"There is a rising tide of opposition and concern about the agenda being pushed by figures in this Tory-led government, and David Cameron must come clean on where the Tories now stand on a woman's right to choose."

The first meetings will examine how pro-choice supporters can reframe the debate, according to Sunny Hundal, editor of the leftwing blog Liberal Conspiracy. Jess McCabe, editor of The F Word blog, is the main organiser of the event.

"It was born out of frustration and as a response to Nadine Dorries's agenda," said Hundal.

"People were not aware until recently about the real threat that is emerging to existing rights, but it's also part of a wider battle against an agenda pushed by the Tories, which includes the role of religious groups in areas like sexual education."

Darinka Aleksic, campaign co-ordinator at Abortion Rights, the national pro-choice campaign, added that the appointment of Life to the forum was a "tipping point" that had galvanised pro-choice supporters growing increasingly concerned about a new threat to the 1967 Abortion Act.

"We have had legal abortion since 1967 so in some ways perhaps we have got used to the idea that it is always going to be there, but the fact is that people are becoming aware that those rights are under threat and need to be protected," she said. "There is a groundswell of support for that protection.

"Things have been quiet since 2008 when there was an attack on the time limit for abortionbut in the last few months a change has been happening."

"That's why we have set up the forum so we move the discussion about sexual health forward. To do this it is only right that a wide range of interests and views are represented."

The Right to Know campaign has stated that the purpose of the Dorries-Field amendment is to ensure that women considering an abortion would be guaranteed access to independent information and advice from someone who had no vested financial interest in the outcome of their decision.

• This article was amended on 6th June. It originally stated that the F Word online magazine was involved in organising the event. It now clarifies that the main organiser is Jess McCabe.